1. Field of the Invention
The present invention relates to a roller suitable for supplying a constant amount of liquid or viscous fluid to a web-fed or sheet-fed plane and a method of manufacturing the roller and, more particularly, to a roller for supplying a constant amount of liquid which is used for, for example, a press when the liquid to be supplied is ink; an offset press when the liquid is dampening water; a printer when the liquid is a dye; a gumming machine when the liquid is paste; and a coating machine when the liquid is coating fluid; and a method of manufacturing the roller. The roller for supplying a constant amount of liquid includes not only a roller for supplying a novel liquid but also a roller for indirectly helping a liquid to be supplied in a constant amount or normally by removing the surplus of the liquid which has once been supplied and returned or non-uniformly distributed portion.
2. Description of the Prior Art
The capacity of a roller for supplying a constant amount of liquid depends on a combination of the roller and a doctor blade for constantly scraping off the surplus of a liquid which has once been supplied, whether the peripheral surface of the roller is even or rough.
For example, when a mesh roller, namely, a roller provided with regular cells on its peripheral surface (the details are described at pp 41 to 45, "New Principle and Practice of Flexographic Press" translated by Japanese Flexographic Technology Association and issued on Mar. 28, 1985), is incorporated into an ink supply system of a press, cells which are the same in size and configuration and are regularly arranged serve as if they were measures, and the surplus ink which adheres to the protrusions is scraped off by a doctor blade, so that only the constant amount of ink within the cells having the same configuration is supplied.
In order to eliminate the non-uniform distribution of the liquid on the roller, there is a phenomenon of the surplus of the ink which has once been supplied to a plate cylinder returning to the ink supply system. To prevent the surplus ink from being mixed with newly supplied ink, the doctor blade is brought into contact with the return side of the peripheral surface of a smooth roller of the ink supply system so as to scrape off the surplus ink or water which returns there (see Japanese Patent Laid-Open No. 44393/1985). PG,4
In both cases described above, when oil ink is used, the peripheral surface of a roller of the ink supply system is coated with copper or a copper alloy which has lipophilic nature in order that the peripheral surface of the roller is ready to receive the oil ink. However, since the hardness of copper or a copper alloy is very low while the hardness of the doctor blade composed of carbon tool steel (SK - 5) is very high, if the peripheral surface coated with copper or copper alloy and the doctor blade are brought into contact with each other, the copper layer wears out too much for a long-term service.
In order to solve this problem, Japanese Patent Laid-Open No. 44393/1985 has proposed a method of spraying porous ceramic onto the peripheral surface of the roller so as to hold the hardness of the layer which can withstand the contact of the blade, while filling the pores with a lipophilic resin which readily absorbs oil ink.
In this case, however, since it is very difficult to provide, for example, regular cells on the peripheral surface of the roller which is uniformly coated with ceramic, it cannot disadvantageously be used as a mesh roller (anilox roller).
Furthermore, since the entire peripheral surface is uniformly coated with ceramic, the doctor blade which is constantly in contact with the peripheral surface wears out in a short time, which frequently requires adjustment of the contact state or replacement of the blade, resulting in waste of materials.
Accordingly, a roller which has both hard portion which is capable of limiting the wear of a doctor blade to its minimum and producing uniform wear without a fear of local wear, and soft portion which facilitates the formation of cells for measuring and the use of lipophilic material has been strongly demanded.